Fasteners & Threads — Cheat Sheet
Preload, torque, tensile area, thread engagement, shear and bearing.
Preload & torque
| Torque | T = K·D·F (K ≈ 0.2 dry, 0.15 lubed) |
| Target preload | F = %·S_p·A_t (typ. 65–90%) |
| Metric tensile area | A_t = (π/4)(d − 0.9382p)² |
Threads
| Engagement (steel) | L_e ≈ 1·D; aluminium ≈ 2·D |
| UNJ / MJ | controlled root radius → better fatigue |
Shear connections
| Pin/bolt shear | τ = F / (n·A), n = 1 single / 2 double |
| Bearing stress | σ_b = F / (d·t) |
Bolted joint
| Load factor | C = k_b / (k_b + k_m) |
| Bolt load | F_bolt = F_i + C·F_e |
| Separation load | F_sep = F_i / (1 − C) |
Welds
| Fillet throat | a = 0.707 · leg |
| Shear stress | τ = P / (0.707·leg·L) |
Formula reference — verify against the governing standard. Not a substitute for engineering judgment.